The proposed experiments will test hypotheses regarding the organization and integration of excitatory and inhibitory inputs to the inferior colliculus (IC) from monaural and binaural sources in the lower brain stem. The IC preserves and transforms information from ten numerous sources before projecting it to the auditory thalamus and cortex. Within the IC, the inputs are organized into one map of best frequency, while different zones within a frequency lamina are composed of different combinations of inputs from the various brain stem structures. We will test hypotheses about how specific inputs are segregated and combined, and how this creates functionally specialized zones within the IC. In Aim 1, anterograde tracer techniques will be used to test if inhibitory projections from the dorsal nucleus of the lateral lemniscus (DNLL) converge with excitatory projections from the medial superior olive (MSO). We will also test whether the DNLL inputs to the IC remain segregated from inhibitory inputs from the lateral superior olive (LSO). In Aim 2, retrograde tracer techniques and IC neurophysiology will used to test the hypothesis that some types of functional specialization in the IC is created by segregated inputs from the MSO, LSO, and dorsal cochlear nucleus (DCN). We will also test the hypothesis that inhibitory inputs from DNLL and LSO sharpen distinct types of binaural tuning.